Phase equilibria and crystal structures of phases in the La-Fe-Ni-O system at 1370 K in air

Abstract

The phase equilibria in the La-Fe-Ni-O system have been studied at 1370 K in air, and the La-Fe-Ni-O phase diagram at constant temperature and pressure has been constructed. Based on x-ray diffraction results for samples prepared by standard solid-state reactions and via citrate and nitrate routes, the following solid solutions have been shown to exist at 1370 K in air: LaFe1 − x Ni x O3 − δ (0 < x ≤ 0.4, sp. gr. Pbnm; 0.6 ≤ x ≤ 0.8, sp. gr. R-3 c), La4(Ni1 − y Fe y )3O10 − δ (0 < y ≤ 0.3), La3(Ni1 − z Fe z )2O7 − δ (0 < z ≤ 0.05), La2Ni1 − v Fe v O4 + δ (0 < v ≤ 0.05), NikFe3 − k O4 (0.81 ≤ k ≤ 1.05), Ni1 − m Fe m O (0 < m ≤ 0.05), and Fe2 − p Ni p O3 (0 < p ≤ 0.04). The lattice constants and structural parameters of single-phase samples have been refined by the Rietveld profile analysis method.